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At some point, your furnace may give off a certain smell that will cause you to worry. It is a sign that your furnace is breaking? Is it a sign of danger?

While some smells from your furnace are normal and no cause for alarm, there are others that point to major and potentially dangerous problems. In this blog post, we’ll explain which odors require immediate attention from an HVAC professional.

Concerning Furnace Odors

These smells are red flags that indicate a serious problem with your furnace. We’ll explain what to do upon encountering each of these odors (aside from contacting an HVAC technician as soon as possible).

Burning Smell

Don’t panic right away--it is fairly normal for your furnace to emit a burning odor after you first start it up, particularly if you haven’t used it in a while. What you’re smelling in this instance is just the dust that built up when the furnace was not in use.

However, if the burning smell continues longer than 24 hours or if it keeps coming back, this is definitely cause for concern. Before contacting a technician, shut off your furnace’s gas supply, and turn your furnace off using the shut-off valve.

Overheating Smell

This smell is a little hard to describe. Some people describe it as electrical, while others compare it to the smell of hot rubber. If you smell an odor like this, it’s possible that your furnace’s motor function is overheating. It’s possible that other electrical functions in your furnace may be overheating as well.

If the odor is similar to burning rubber, part of your furnace might even be burning. To prevent the problem from worsening and causing a fire, turn off your HVAC unit. Don’t attempt to access the unit’s interior, as there is most likely an electrical issue that should only be handled with proper equipment.

Sulfurous, Rotten Egg Smell

If you smell this odor in your home, then you have a gas leak. Natural gas is actually odorless, but a harmless chemical called mercaptan is added to it as a safety feature. Without mercaptan lending natural gas that distinct smell, you probably would never be able to detect leaking gas in your home before something would inevitably ignite it.

Once you get a whiff of that rotten egg smell, make sure everyone evacuates the house before you call your gas company. Stay in a safe place until technicians have repaired the leak. After this, contact an HVAC technician to perform a maintenance check on your furnace. It’s possible that the furnace will need to be repaired or replaced entirely, depending on the severity of the problem.

Musty, Mildew Smell

This smell does indicate a problem but with a different part of your HVAC system: your air ducts. Moisture can travel into your air ducts and accumulate there, leading to mold growth. The mold creates that musty smell, and when air blows through the air ducts, it blows the smell--and the mold spores--throughout your home.

Mold spores can attach to other surfaces in your home and create more mold growth. This is part of a cycle that poses a serious risk to your family’s indoor air quality, particularly if anyone in your household already suffers from a respiratory condition. To prevent these mold problems, it’s best to contact an HVAC technician for a professional air duct cleaning.

If you are concerned about any strange smells coming from your HVAC system, don’t hesitate to contact our HVAC professionals. Moe Plumbing’s HVAC experts have been providing residential customers with heating and air conditioning services since 1927. We’re honored to have received the Angie’sList “Super Service Award” and look forward to serving you.